Split tower for a bone anchor

ABSTRACT

An anchor extender can be couplable to a bone anchor and can include an outer sleeve, an inner sleeve, and a lock. The lock can be operable to translate the inner sleeve relative to the outer sleeve between a locked position and an unlocked position to secure the inner sleeve and the outer sleeve to a head of the bone anchor in the locked position and to release the inner sleeve and the outer sleeve from the head of the bone anchor in the unlocked position.

CLAIM OF PRIORITY

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/779,255, filed on Dec. 13, 2018, the benefit ofpriority of which is claimed hereby, and which is incorporated byreference herein in its entirety.

BACKGROUND

Orthopedic devices such as rods, plates, tethers, staples, and otherdevices can be used in various spinal procedures to correctabnormalities (e.g., scoliosis) or to address injuries (e.g., vertebralfracture). In some spinal procedures, anchors and rods can be securedalong a spinal column between one or more vertebrae to stabilize aregion of the spine. Some surgical procedures performed on the spinalcolumn using such devices have become less invasive. However, somespecial parts used in minimally-invasive spinal procedures can increasethe difficulty of the installation procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1A illustrates a front view of a tower assembly in a firstcondition, in accordance with at least one example of this disclosure.

FIG. 1B illustrates a front view of a tower assembly in a secondcondition, in accordance with at least one example of this disclosure.

FIG. 1C illustrates a front view of a tower assembly in a thirdcondition, in accordance with at least one example of this disclosure.

FIG. 2 illustrates an exploded isometric view of an anchor assembly, inaccordance with at least one example of this disclosure.

FIG. 3A illustrates an isometric view of a tower assembly in a firstcondition, in accordance with at least one example of this disclosure.

FIG. 3B illustrates an isometric view of a tower assembly in a secondcondition, in accordance with at least one example of this disclosure.

FIG. 3C illustrates a focused isometric view of a tower assembly in asecond condition, in accordance with at least one example of thisdisclosure.

FIG. 3D illustrates an isometric view of a tower assembly in a thirdcondition, in accordance with at least one example of this disclosure.

FIG. 3E illustrates a focused isometric view of a tower assembly in athird condition, in accordance with at least one example of thisdisclosure.

FIG. 4A illustrates a side view of a portion of a tower assembly, inaccordance with at least one example of this disclosure.

FIG. 4B illustrates an isometric view of a portion of a tower assembly,in accordance with at least one example of this disclosure.

FIG. 4C illustrates a focused rear view of a tower assembly in a firstcondition, in accordance with at least one example of this disclosure.

FIG. 4D illustrates a focused rear view of a tower assembly in a secondcondition, in accordance with at least one example of this disclosure.

FIG. 5 illustrates an isometric view of a portion of a tower assembly,in accordance with at least one example of this disclosure.

FIG. 6 illustrates a side view of a cross-section of a portion of atower assembly, in accordance with at least one example of thisdisclosure.

DETAILED DESCRIPTION

Bone anchors can be used together with connecting members (such as rigidand semi-rigid rods) to straighten a region of a human spine to addressa spinal abnormality (e.g., scoliosis), to stabilize a spine followingan injury (e.g., fractured vertebrae), or to address degeneration of thespine caused by disease. In minimally invasive spinal procedures toaddress these issues, multiple small incisions can be made to formmultiple small cavities near individual vertebrae. A large amount of theprocedure can be performed through manipulation of instruments andcomponents extending through the small surgical cavities using specialinstruments that are able to be manipulated from outside of thecavities.

For example, anchors are commonly driven into vertebrae, where theanchors include extensions coupled to the anchors and where theextensions have a length sufficient to extend outside of the cavity sothat the anchors (and components engaging the anchors) can bemanipulated from outside of the cavities. In some of these devices,extended tabs of the anchors can be used to extend through the cavities,which often must be separable from the heads of the anchors (whichremain secured to vertebrae). Further, because the extensions often needto receive a connecting member and a closure top (or set screw), theextensions must often be of a quantity of at least two to allowthreading of the closure top into the head of the anchor and to providea slot to reduce and retain the connecting member.

Some designs include two extensions each coupled to the head of theanchor at a breakaway portion, where each extended tab can beindividually bent to allow separation of the extension from the head atthe breakaway portions. This design requires relative movement of theextended tabs for separation. However, the extended tabs must also berigid enough to transfer forces between the tabs and the head. Forexample, sometimes forces must be transferred from a portion of theextended tabs external to the cavity to a portion of the extended tabsinto the cavity and ultimately to the head and/or shank of the anchor.However, such operations can cause undesired separation of the extensionor extended tab from the anchor, which can increase a risk of materialbeing lost into a cavity and can add another step to the procedure.

Other designs include towers that are releasably connected to theanchors. Many of these designs are connected to the anchor at an angle.Some of these designs also require a single-piece assembly including arigid and closed top, which can obstruct vision down the anchor and intothe cavity during an operation. This disclosure addresses problems withexisting towers and extended tab designs by providing a split towerassembly that is releasably securable to a head or housing of theanchor. The split tower can be sufficiently rigid to allow for transferof forces from the tower external to an opening and down to an anchorwhile limiting unwanted separation from the anchor.

Because of the tower assembly's split design and quick, separablelocking mechanism, the tower can be relatively quickly removable fromthe anchor to allow the tower assembly to be easily removed from theopening following use of the tower for reduction (for example). Becausea cap of the tower can be easily removed at any time, the tower can helpimprove visualization of components within the opening (e.g., anchor,connecting rod, and/or set screw) during the operation.

Also, by providing a relatively straight split tower assembly, the towerassembly can help to reduce stretching of the surgical site. And,because the tower assembly can be removed straight out of an opening(for example, without significant side to side movement for breaking anextended tab), stretching can be further reduced.

FIG. 1A illustrates a front view of a tower assembly 100 in a firstcondition, in accordance with at least one example of this disclosure.FIG. 1B illustrates a front view of the tower assembly 100 in a secondcondition, in accordance with at least one example of this disclosure.FIG. 1C illustrates a front view of the tower assembly 100 in a thirdcondition, in accordance with at least one example of this disclosure.FIGS. 1A-1C are discussed below concurrently.

The tower assembly 100 can include a tower 102 and an anchor 104. Theanchor 104 can include a shank 106, and a head or housing 108. The tower102 can include arms 110A and 110B (collectively referred to as arms110), locks 112A and 112B (collective referred to as locks 112), and acap 114. Each lock 112 can include a lever 116 and a cam 118. The cap114 can include a proximal portion 120 and a distal portion 122. Theproximal portion 120 can include a knob 124. The distal portion 122 caninclude eyes 126A and 126B. Each of the arms 110 can include a proximalprojection 128 (128A and 128B) (shown in FIGS. 1B and 1C). The arms 110can form channels 130 and the head 104 can form channels 132. Also shownin FIGS. 1A-1C are axis A and orientation indicators Proximal andDistal. Also shown in FIG. 1B is a connecting member 134.

Each component of the tower 102 and the anchor 104 can be comprised ofrigid and semi-rigid materials such as metals, plastics, composites, orthe like. In some examples, the tower 102 and/or the anchor 104 can becomprised of bio-compatible materials, such as stainless steel,titanium, or the like. In some examples, the tower 102 and/or the anchor104 can be comprised of only one material, and can be comprised ofmultiple materials in other examples.

The head 108 of the anchor 104 can be coupled to the shank 106 at adistal portion of the head 108 with the shank 106 extending distallytherefrom and where the axis A can be a central axis for the head 108and the shank 106. In other examples, the shank 106 can deviate from theaxis A at various angles. The shank 106 can be a threaded shank or screwincluding male threads configured to engage bone, such as a relativelycoarse thread pattern. The head 108 of the anchor 104 can form thechannels 132, which can be generally U-shaped channels alignable withthe channels 130 of the arms 110, which can each be configured toreceive the connecting member 134 therethrough.

In some examples, the shank 106 can be configured to threadably secureto a vertebra of a spine of a human. The shank 106 can be an integralcomponent to the head 110 in some examples, coupled to a distal portionof the head 110. In other examples, the shank 160 can be a portion of afastener that is a separate component from the head 110 and can bedisposed within a bore of the head 110 and configured to be retainedtherein.

The arms 110A and 110B can be generally elongate members extendingsubstantially parallel to axis A when coupled to the head 108 of theanchor 104. As discussed below in further detail, each of the arms 110can include an inner sleeve and an outer sleeve, where the sleeves canbe translated relatively to lock the arms 110 to the head 108individually at a distal portion of each of the arms 110. Together thearms 110 can define the channels 130, which can align with the channels132 of the head 108 of the anchor 104 when the arms 110 are secured tothe anchor 104. In some examples, the channels 130 and 132 can beconfigured to receive the connecting member 134 therethrough. Theproximal projections 128 can be projections extending radially outwardfrom the inner sleeve of the arms 110 and can be sized and shaped tocouple to the eyes 126 of the distal portion 122 of the cap 114.

The locks 112A and 112B can be secured to a proximal portion each thearms 110A and 110B, respectively. For example, the lever 116A can besecured to the cam 118A, where the cam 118A can be coupled to a proximalportion of the arm 110A. As discussed below, the levers 118 can beoperable to move the cams 116 to individually lock and unlock the arms110 to the head 108 of the anchor 108.

The knob 124 can be an actuator coupled to the proximal portion of thecap 114. The knob 124 can be knurled in some examples, and can haveother surface finishes to improve grip (such as milling textures). Thedistal portion 122 can include eyes 126A and 126B, which can be openingsin the distal portion 122. The knob 124 can be coupled to a threadedpiston within the cap 114 and the knob 124 can be rotatable relative tothe cap 114 to translate the piston with respect to the cap 114 and theknob 124. Also shown on the cap 114 are tool bores 136, which can bebores in a body of the cap 114 configured to receive a portion of a tooltherein for mounting of the tool to the cap 114.

In operation of some examples, the distal portion of the arm 110A can besecured to the head 108 by engaging the distal portion of the arm 110Awith the head 108 and by operating the lock 112A to secure the arm 110Ato the anchor 104, as shown in FIG. 1A. In some examples, the arm 110Acan be secured to the head 108 before the tower assembly 100 is insertedinto an opening. In other examples, the arm 110A can be secured to thehead 108 after the shank 106 is secured to a bone of a patient.

After securing a first of the arms 110, a second arm can be secured tothe anchor 104. For example, the distal portion of the arm 110B can besecured to the head 108 by engaging the distal portion of the arm 110Bwith the head 108 and by operating the lock 112B to secure the arm 110Bto the anchor 104, as shown in FIG. 1B. In some examples, the tower 102and anchor 104 can be inserted into an opening of a patient followingsecuring of the arms 110 to the head 108. Because the channels 130 areopen from a proximal perspective, the tower assembly can help providerelatively easy insertion of tools into the head 108 and can provide animproved viewing perspective. In some examples, after securing the arms110 to the anchor, the arms 110 (or the channels 130 of the arms 110)can be used to guide the connecting member 134 into the channels 130 andinto the channels 132 of the anchor 104. In other examples, the tower102 can be inserted into a cavity before the connecting member isinserted into the channels 130.

Once the arms 110 are secured to the anchor 104, the cap 114 can besecured to the arms 110. The proximal projections 128A and 128B can beinserted into a distal opening of the cap 114 until a distal portion ofthe cap 114 contacts a proximal portion of the outer sleeve. The knob124 can then be rotated (for example in a clock-wise direction aboutaxis A from a proximal perspective) to translate the piston within thecap 114 distally. The piston can engage a radially inner portion of theproximal projections 128A and 128B to force the proximal projections128A and 128B radially outward into the eyes 126A and 126B. The pistoncan thereby prevent radially inward movement of the proximal projections128A and 128B with respect to the cap 114 when the piston is translateddistally. In such a position, the proximal projections 128A and 128B cancontact the eyes 126A and 126B, respectively, to limit translation ofthe arms 110 with respect to the cap 114, securing the arms 110A and110B to each other and to the cap 114, and helping to transfer forcesbetween the head 108, the arms 110, and the cap 114. Because the levers116 can be operated to lock the arms 110 to the head 108 by hand andbecause the knob 124 can be operated to secure the cap 114 to the arms110 by hand, the tower 102 can be secured to the head 108 withoutadditional or specialized tooling.

In some examples, the connecting member 134 can be inserted into thechannel 130 and translated distally into the channel 132 of the head 108following securing of the cap 114 to the arms 110. In some examples, theshank 106 can be secured to a bone of a patient before or after any ofthe steps discussed above. In further examples, the arms 110 can be usedto apply a force on the anchor 102 to manipulate a position of the boneof the patient, such as during a de-rotation procedure.

Once the connection member 134 and shank 106 are in place, a set screwcan be inserted into the channel 130 and can be secured to the channels132 of the head 108 to retain the connecting member 134 within the head108. In some examples, the connection member 134 can be reduced (orforced) distally by the set screw from the channels 130 of the arms 110into the channels 132 of the head 108. During such a process, the cap114 can help prevent separation or splaying of the arms 110.

After the anchor 104 is positioned as desired, the tower 102 can beremoved by reversing the steps discussed above. The knob 124 can berotated counter-clockwise to release the proximal projections 128 fromthe cap 114 and the cap 114 can be removed from the arms 110. The lock112B can then be operated to unlock the distal portion of the arm 110Bfrom the head 108 and the arm 110B can be separated from the head 108and removed from the opening. The lock 112A can then be operated tounlock the distal portion of the arm 110A from the head 108 and the arm110A can be separated from the head 108 and removed from the opening.The arms 110 can be removed in any order. In some examples, the anchor104 can be manipulated using only one of the arms 110. In some examples,a single arm, such as the arm 110A, can be used to guide reduction ofthe connection member 134 and/or the set screw.

FIG. 2 illustrates an exploded isometric view the anchor assembly 100,in accordance with at least one example of this disclosure. The anchorassembly 100 can include the arm 110 and the lock 112. The arm 110 caninclude an inner sleeve 140 and an outer sleeve 142. The lock 112 caninclude the lever 116, the cam 118, a cam pin 144, and a lever pin 146.The lever 116 can include a lever pin bore 148, and the cam 118 caninclude cam pin bores 150, and a cam pin groove 152. The inner sleeve140 can include a projection bore 154 and a distal portion 155 of theinner sleeve 140 can include distal projections 156A and 156B. The outersleeve 142 can include a cam bore 158, a collar 160, a sleeve pin bore162, and a distal portion 164 including a distal hook 166.

The cam pin 144 and the lever pin 146 can be rigid or semi-rigidfasteners configured to secured the lever 116 to the cam 118 and the cam118 to the outer sleeve 142, respectively. In some examples, the cam pin144 and the lever pin 146 can be pins, but can be other types offasteners, such as screws or bolts, in other examples.

The cam bore 158 can be a bore in the collar 160 of the outer sleeve142, where the cam bore 158 extends through the outer sleeve 142substantially orthogonally to the axis A. The sleeve pin bore 162 canintersect with the cam bore 158 and can be sized to receive the cam pin144 therein. The lever pin bore 148 can be a bore extending through ahead of the lever 116 and configured to receive the lever pin 146therethrough. Similarly, the cam pin bores 150 can be bores extendingthrough the cam 118. The cam pin groove 152 can be a groove extendingaround a part of a circumference of the cam 118 and configured toreceive and retain a portion of the cam pin 144 therein. The projectionbore 154 can be a bore extending through the inner sleeve 154 proximatea proximal portion of the inner sleeve 140.

In assembly of some examples, the inner sleeve 140 and the outer sleeve142 can each extend along the axis A. In some examples, the inner sleeve140 can be inserted into the outer sleeve 142 until the projection bore154 at least partially aligns with the cam bore 162. The cam 118 canthen be inserted into the cam bore 158 of the collar 160 of the outersleeve 142 such that a projection of the cam 118 extends into theprojection bore 154. The cam pin 144 can then be inserted through thesleeve pin bore 162 and partially into the cam pin groove 152 to retainthe cam 118 within the cam bore 158.

Either before or after the cam 118 is secured to the outer sleeve, ahead of the lever 116 can be inserted into a notch in the cam 118 andthe lever pin 146 can be inserted into the cam pin bore 150 and thelever pin bore 148 to secure the lever 116 to the cam 118 and thereforeto the outer sleeve 142.

The distal projections 156A and 156B can be projections extendingdistally from the distal portion 155 of the inner sleeve 140. In someexamples, the distal projections 156A and 156B can be kidney-shaped,bean-shaped, oval-shaped, or the like. The distal hook 166 of the distalportion 164 can be a hook extending distally and radially inward fromthe distal portion 164 of the outer sleeve 142. The distal projections156A and 156B and the distal hook 166 are discussed further below withrespect to FIGS. 3A-3E.

FIG. 3A illustrates an isometric view of the tower assembly 100 in afirst condition, in accordance with at least one example of thisdisclosure. FIG. 3B illustrates an isometric view of the tower assembly100 in a second condition, in accordance with at least one example ofthis disclosure. FIG. 3C illustrates a focused isometric view of thetower assembly 100 in a second condition indicated by indicator 3C ofFIG. 3B, in accordance with at least one example of this disclosure.FIG. 3D illustrates an isometric view of the tower assembly 100 in athird condition, in accordance with at least one example of thisdisclosure. FIG. 3E illustrates a focused isometric view of the towerassembly 100 in a third condition indicated by indicator 3E of FIG. 3D,in accordance with at least one example of this disclosure. FIGS. 3A-3Eare discussed below concurrently.

The components of the tower assembly 100 can be consistent with FIGS.1A-2 above; FIGS. 3A-3E show additional details of, and interactionsbetween, the components of the tower assembly 100. For example, FIG. 3Ashows lever 116 in an unlocked position and shows an internal surface117 of the lever 116, where the internal surface 117 can be shaped tomatch an outer surface of the outer sleeve 142 so that the lever 116 canrest against the outer surface of the outer sleeve 142. Also, aperiphery of the lever 116 can have a reduced thickness to help allowthe lever 116 to be grasped when the lever is in the locked position andresting on the outer sleeve 142.

FIG. 3B shows the lever 116 in the unlocked position, but shows thedistal hook 166 engaged with a slot 168 of the head 108 of the anchor104. In some examples, the slot 168 can be a channel or slot extendingradially into the head 108 of the anchor. The slot 168 can be sized toreceive the distal hook 166 therein and can include proximal and distalflats configured to contact the distal hook 166 to help prevent axialtranslation of the arm 110 with respect to the head 108. In someexamples, the inner sleeve 140 and/or the outer sleeve 142 can have aradius of curvature configured to mate with an outer surface of the head108.

FIGS. 3B and 3C also show distal projections 156A and 156B, which can bealigned with proximal bores 170A and 170B, respectively, when the hook166 is secured to one of the channels 168 of the head 108. The proximalbores 170A and 170B can extend into a proximal portion 172 from aproximal surface of the head 108. The proximal bores 170A and 170B canbe sized and shaped complimentary to the distal projections 156A and156B. That is, the proximal bores 170A and 170B can be oval-shaped,bean-shaped, kidney-shaped, or the like.

FIGS. 3D and 3E shows the tower assembly 100 in a third condition wherethe distal hook 166 remains inserted into or engaged with the channel168 of the head 108 of the anchor 104. When the inner sleeve istranslated distally by rotating the lever 116 in a direction D (shown inFIG. 3B), the distal projections 156A and 156B are translated into theproximal bores 170A and 170B, and the distal portion 155 of the innersleeve 140 can be in contact with the proximal portion 172 of the head108. Because the distal hook 166 can apply a distal-to-proximal force onthe head 108 and because the distal portion 155 can provide aproximal-to-distal force on the proximal portion 172 of the head 108,the head 108 is pinched by the inner sleeve 140 and the outer sleeve142, helping to prevent proximal and distal translation of the arm 110with respect to the head 108.

Further, because the distal projections 156A and 156B are disposed inthe proximal bores 170A and 170B when the inner sleeve is translateddistally, the sleeve 110 is substantially prevented from moving radially(or non-axially) with respect to the head 108. This arrangement can helpprevent the arm 110 from unintentionally separating from the head 108.

Though the example above is discussed as including the channel 168 toreceive the distal hook 166, the tower assembly 100 can be configured toconnect to any screw or fastener including a ledge, shelf, or bore. Forexample, the distal hook 166 can be configured to retain a standardscrew head in some examples. In some examples, the arms 110 can includeadditional projections or hooks to engage additional bores or grooves ona fastener to help reduce rotation of the fastener with respect to thearms 110.

FIG. 4A illustrates a side view of a portion of the tower assembly 100,in accordance with at least one example of this disclosure. FIG. 4Billustrates an isometric view of the cam 118, in accordance with atleast one example of this disclosure. FIG. 4C illustrates a focused rearview of the tower assembly 100 in a first condition, in accordance withat least one example of this disclosure. FIG. 4D illustrates a focusedrear view of the tower assembly 100 in a second condition, in accordancewith at least one example of this disclosure. FIGS. 4A-4D are discussedbelow concurrently.

The components of the tower assembly 100 shown in FIGS. 4A-4D can beconsistent with those discussed above with respect to FIGS. 1A-3E; FIGS.4A-4D show additional details of the tower assembly 100. For example,FIG. 3A shows cam 118 disposed within the cam bore 158 of the collar 160of the outer sleeve 142. FIG. 3A also shows the cam pin 146 securing thecam 118 to the collar 160.

FIG. 4B shows a projection 176 of the cam 118, which can have agenerally oval shape, elliptical shape, rounded rectangular prism shape,or the like. The projection 176 can be a boss, in some examples,extending from a surface of the cam 118 substantially orthogonally tothe axis A when the cam is inserted into the bore 158 of the collar 160.In some examples, the projection 176 can have an inner side 178 and anouter side 180. In some examples, the inner side 178 and the outer side180 can have the same geometry. In other examples, the outer side 178can be different from the inner side 180, such as a relatively flattershape to help limit accidental rotation of the cam 118.

FIG. 4B also shows the pin channel 152 of the cam 118, which can extendaround most of a circumference of the cam 118, but can terminate at pinstop 153. The pin stop 153 can be configured to contact the cam pin 144to limit rotation of the cam 118 relative to the outer sleeve 142. Thecam 118 can include a second pin stop to limit rotation of the cam 118in a second rotational direction.

FIG. 4B further shows a lever notch 182, which can be a notch sized andshaped to receive a head of the lever 116. The cam pin bore 150 canintersect with the lever notch 182 so that the lever pin bore 148 canreceive the lever pin 146 therethrough to secure the lever 116 to thecam 118. The lever notch 182 can also be sized and shaped to allow thelever 116 to rotate about the lever pin 146 with respect to the cam 118.

FIGS. 4C and 4D show how the cam 118, the inner sleeve 140, and theouter sleeve 142 work together to translate the inner sleeve 140. Theprojection bore 154 can include a proximal wall 184 and a distal wall186. In operation of some examples, when the lever 116 is in theunlocked position (as shown in FIGS. 3A and 3B), the projection 176 canbe oriented in a proximal position such that the outer surface 180 ofthe projection 176 rests against the proximal wall 184 and the innersurface 178 rests against the distal wall 186 of the projection bore154.

The lever 116 can then be rotated as indicated by direction D of FIG. 3Bcausing the cam 118 to rotate counter-clockwise with respect to FIGS. 4Cand 4D. During rotation of the cam 118, the projection 176 also rotateswith respect to the inner sleeve 140 and the outer sleeve 142. Duringrotation, the projection 176 contacts the walls of the projection bore154, causing the inner sleeve 140 to translate distally as the cam isrotated 180 degrees until a side wall 187 of the projection 176 contactsa wall 189 of the projection bore 154. In some examples, the cam pin 144can contact the pin stop 153 to help limit rotation of the cam 118. Oncethe cam 118 can no longer rotate, the lever 116 can be pressed downtoward the outer sleeve 142.

In such an arrangement, the projection 176 can be compressed inward atthe outer surface 180 and the inner surface 178 by the inner sleeve 140to create a friction fit between the inner sleeve 140 and the projection176 to help prevent accidental rotation of the cam 118 with respect tothe sleeve. In some examples, a side wall 187 of the projection 176 anda side wall 189 of the projection bore 154 can both engage in the lockedposition to create a flat-to-flat engagement to limit accidentalrotation of the cam 118.

When the lever 116 is pivoted downward to rest against the outer arm, aneck or head of the lever 116 can be engaged with a notch 188 of thecollar 160. Engagement of the lever 116 and the notch 188 of the collar160 can help limit rotation of the cam 118 with respect to the outersleeve 142 when the lever 116 is in the downward or locked position tohelp prevent accidental unlocking of the arm 110 from the head 108.

When it is desired to unlock the arm 110 from the head 108, the lever116 can be lifted off the arm 110 by pivoting the lever about the leverpin 146. The lever 116 can then be rotated to cause rotation of the cam118 to move the projection 176 in a clock-wise rotational direction withrespect to FIGS. 4C and 4D to translate the inner sleeve 140 proximallywith respect to the outer sleeve 142. Such a process can be repeated asdesired.

FIGS. 4C and 4D also show chamfers 190 and 192 of the inner sleeve 140.The chamfers 190 and 192 can be chamfered edges extending parallel withlongitudinal axis of the inner sleeve 140. The outer sleeve 142 caninclude a pair of opposing rails 194 and 196 configured to receive thechamfers 190 and 192 therein to create a sliding engagement between theinner sleeve 140 and the outer sleeve 142. The engagement between thechamfers 190 and 192 and the rails 194 and 196 can help to guidetranslation and prevent non-translation movement of the inner sleeve 140within the outer sleeve 142.

Though FIGS. 4A-4D describe the lock 112 as including cam 118 as beingoperable to translate the inner sleeve 140 with respect to the outersleeve 142, other examples can include other components that can performsuch operations. For example, the lock 112 can include a worm driveengageable with one or both of the inner sleeve 140 and the outer sleeve142 where the worm drive can be rotatable to translate the inner sleeve140 with respect to the outer sleeve 142. In other similar examples,other gears can be used. In other examples, the lock 112 can include abiasing element, such as a spring, to bias the inner sleeve 140 withrespect to the outer sleeve 142. In further examples, the lock caninclude a collar or ring to engage a threaded portion of one of thesleeves to cause the inner sleeve 140 to translate with respect to theouter sleeve 142.

FIG. 5 illustrates an isometric view of the lever 516, in accordancewith at least one example of this disclosure. The lever 516 can includea pin bore 548, a body 550, a head 552, a neck 554, a living hinge 556(adjacent a gap 558), and a chamfer 560. Also shown in FIG. 5 is anangle θ and orientation indicators Proximal and Distal.

The lever 516 can be consistent with the lever 116 discussed above;however, FIG. 5 shows additional details of the lever 516. For example,FIG. 5 shows how the body 550 of the lever can connect to the head 552via the neck 554, which can be angled to offset the head 552 from thebody 550 for attachment to the cam 118.

FIG. 5 also shows the living hinge 556 (or living spring), which can bespaced from the head 552 by the gap 558. The living hinge can becantilevered from the head 552, such that the living hinge 556 candeflect with respect to the head 552. In some examples, the living hinge556 can be under compression in the locked and the unlocked position tohelp prevent the lever 116 from moving without interaction by a user.Though the living hinge 556 is discussed as being a living hinge coupledto the head 552, the living hinge 556 can be other types of biasingelements, such as a spring or bar.

FIG. 6 illustrates a side view of a cross-section of a portion of atower assembly 600, in accordance with at least one example of thisdisclosure. The tower assembly 600 can include a cap having a piston anda pair of pins each configured to engage a sleeve of an extender tosecure the cap to the extenders and can provide a tool-less interfacefor quickly securing the cap to the extensions for transfer of forcesbetween the extensions and the cap. Such a cap can be included in any ofthe embodiments discussed above.

The tower assembly 600 can be similar to the tower assembly 100discussed above with respect to FIGS. 1-5 ; similar components cantherefore include similar reference numerals and names. The towerassembly 600 can include a first arm 610A, a second arm 610B, a firstlock 612A, a second lock 612B, and a cap 614. The first arm 610A caninclude an inner sleeve 640A and an outer sleeve 642A. The second arm610B can include an inner sleeve 640B and an outer sleeve 642B. Thefirst lock 612A can include a lever 616A and a cam 618A. The second lock612B can include a lever 616B and a cam 618B. The first inner sleeve640A can include a proximal projection 628A, a chamfer 649A, and a pinbore 651A. The second inner sleeve 640B can include, a chamfer 649B, aproximal projection 628B and a pin bore 651B. The first lever 616A caninclude a head 652A and living hinge 656 and the first cam 618A caninclude a hinge slot 653A. The second lever 616B can include a head 652Band living hinge 656 and the first cam 618B can include a hinge slot653B. The cap 614 can include a knob 624, a body 625 (including a bore627), eyes 626A and 626B, a piston 629, a collar 631, and pins 633(shown as pin 633A and pin 633B). The bore 627 can include a threadedportion 635. The piston 629 can include a threaded portion 637, a distalchamfer 639, and a proximal portion 641. The knob 624 can include a toolinterface 643. Also shown in FIG. 6 are axis A and orientationindicators Proximal and Distal.

The proximal projection 628A and the proximal projection 628B of theinner sleeves 640A and 640B, respectively, can each be radiallyextending proximal projections extend from a radially outer portion ofthe inner sleeves 640A and 640B, respectively. The proximal projection628A and the proximal projection 628B can be configured to insert intothe eyes 626A and 626B, respectively of the cap 614.

The chamfer 649A and the chamfer 649B of the inner sleeves 640A and640B, respectively, can be chamfers extending radially inward from aproximal portion of the inner sleeves 640A and 640B and can each becomplimentary to the distal chamfer 639 of the piston 629. The pin bore651A and the pin bore 651B of each of the inner sleeves 640A and 640B,respectively, can be bores extending through each of the inner sleeves640A and 640B, respectively, and can each configured to receive one ofthe pins 633 therethrough to limit axial movement of the inner sleeves640 with respect to the cap 614 and the outer sleeves 642.

The knob 624 can be an actuator coupled to the proximal portion of thecap body 625 and can be rotatable relative to the body 625. The knob 624can be knurled in some examples, and can have other surface finishes toimprove grip (such as milling textures). A bore of the knob 624 can beconfigured to receive and retain the proximal portion 641 of the piston629 therein such that the knob 624 can be rotatable with the piston 629.The tool interface 643 can be a recess or bore extending into a proximalportion of the knob 624 and can be sized and shaped to receive a tooltherein for application of torque to the knob 624. The tool interfacecan be hex, cross-recess, square, hexalobular, or the like. The distalchamfer 639 of the piston 629 can be a chamfer extending radially inwardfrom a radially outer surface of a distal portion of the piston 629 andcan be configured to engage the chamfers 649 of the inner sleeves 640.

The body 625 can include the bore 627 which can extend through the body625 long the axis A. The threaded portion 635 of the body can be at adistal portion of the bore 627 and can be configured to threadablyengage the threaded portion 637 of the piston such that rotation of theknob 624 and therefore the piston 641 can cause the piston to threadinto and out of the bore 627 of the body 625, causing translation of thepiston 627 with respect to the body 625. The knob 624 can also translatewith respect to the body 625.

The collar 631 can extend distally from a distal portion of the body 625and can extend radially outward from the body 625 to have a largerdiameter than the body 625. The collar 631 can include a bore to receivethe inner sleeve 640 therein. The collar 631 can, at least in part, formthe eyes 626A and 626B, which can be bores or openings extending throughthe collar 631 and/or the body 625. The eyes 626 can be sized and shapedto receive the proximal projections 628 therein. The pins 633 can berigid or semi-rigid members connected to the collar 631 and extendingradially inward therefrom.

In operation, when the extensions 610 are in a locked position, as shownin FIG. 6 , the proximal portions of the inner sleeves 640 can beinserted into the collar 631 distally-to-proximally until the proximalprojections 628 engage the body 625 and/or until the proximalprojections 628 engage the piston 629 and/or until the outer sleeves 642engage a distal portion of the collar 631. The engagement(s) can alignthe proximal projections 628 with the eyes 626 and can align the pins633 with the pin bores 651.

Following insertion of the inner sleeves 640 into the collar 631, theknob 624 can be rotated to translate the knob 624 and the piston 629distally via the threaded engagement between the piston 629 and the body625. The piston 629 can translate distally such that the chamfer 639 ofthe piston 629 engages the chamfers 649 of the inner sleeves 640, wherethe engagement can force the proximal projection 628A and 628B radiallyoutward into the eyes 626A and 626B, respectively, to secure the cap 614to the extenders 610. The engagement of the chamfer 639 of the piston629 and the chamfers 649 of the inner sleeves 640 can also cause thepins 633 to each extend into the pin bores 651 to help limit axialtranslation of the inner sleeves 640 with respect to the cap 614. Thepiston 629 can be limited in distal translation via contact of theproximal portions 628 with the collar 630 and/or via contact of the pinbores 651 with the pins 633 and/or via contact between the knob 624 andthe body 625. Contact between these components can also preventdistal-to-proximal translation of the cap with respect to the extensions610 when the piston 629 is translated distally, as shown in FIG. 6 ,helping to prevent separation of the cap 614 from the extensions andhelping to transfer forces between the cap 614 and the extensions 610.

When it is desired to remove the cap 614, the knob 624 can be rotated ina direction opposite the locking direction to translate the knob 624 andthe piston 629 proximally, allowing the proximal projections 626 to moveradially inward from the eyes 628 and allowing the pins 633 to disengagefrom the pin bores 651 so that the cap 624 can be removed from theextensions 610. Such a process can be repeated as desired.

FIG. 6 also shows how the living hinge 656 can engage with the hingeslot 653A of the first cam 618A. The hinge slot 653A can be shaped toreceive and retain the living hinge 656 and to help the living hinge 656bias the lever 616A away from the outer sleeve 642A.

NOTES AND EXAMPLES

The following, non-limiting examples, detail certain aspects of thepresent subject matter to solve the challenges and provide the benefitsdiscussed herein, among others.

Example 1 is an anchor extender couplable to a bone anchor, the anchorextender comprising: an outer sleeve extending along a longitudinal axisfrom a proximal portion to a distal portion, the distal portionengageable with a head of a bone anchor; an inner sleeve extending alonga longitudinal axis from a proximal portion to a distal portion, theinner sleeve nestable within the outer sleeve; and a lock engageablewith the outer sleeve and the inner sleeve, the lock including a camdisposable in the outer sleeve and rotatable therein, the cam rotatableto translate the inner sleeve relative to the outer sleeve between alocked position and an unlocked position to secure the inner sleeve andthe outer sleeve to the head of the bone anchor in the locked positionand to release the inner sleeve and the outer sleeve from the head ofthe bone anchor in the unlocked position, the lock comprising: a levercouplable to the cam, wherein the lever is operable to rotate the cam,and wherein the lever is rotatable relative to the cam to secure the camin the locked position, the lever including a living spring engageablewith the cam to bias the lever away from the outer sleeve.

In Example 2, the subject matter of Example 1 optionally includeswherein the proximal portion of the outer sleeve includes an outer boreextending therethrough substantially orthogonally to the longitudinalaxis, the outer bore configured to receive the cam therein.

In Example 3, the subject matter of Example 2 optionally includeswherein the cam includes a boss extending substantially orthogonally tothe longitudinal axis, wherein the inner sleeve includes an inner borealignable with the outer bore, the inner bore configured to receive theboss therein.

In Example 4, the subject matter of Example 3 optionally includeswherein the outer sleeve includes a collar at least partiallysurrounding the outer bore, wherein the cam includes a circumferentialgroove, and wherein the collar is configured to receive a pintherethrough to extender the circumferential groove to guide rotation ofthe cam relative to the outer sleeve.

In Example 5, the subject matter of any one or more of Examples 1-4optionally include wherein the distal portion of the outer sleeveincludes a distal hook extending radially inward and engageable with anotch in an outer surface of the head of the bone anchor.

In Example 6, the subject matter of Example 5 optionally includeswherein the distal portion of the inner sleeve includes a distalprojection extending axially distally and insertable into a bore in aproximal portion of the head of the anchor when the inner sleeve is inthe locked position.

In Example 7, the subject matter of Example 6 optionally includeswherein engagement of the distal hook with the notch of the head in theunlocked position aligns the distal projection with the bore of theproximal portion of the head.

In Example 8, the subject matter of any one or more of Examples 1-7optionally include wherein the inner sleeve includes chamfered radiallyinner edges extending along the longitudinal axis and wherein the outersleeve includes a pair of opposing rails configured to receive thechamfered edges therein to create a sliding engagement between the innersleeve and the outer sleeve.

In Example 9, the subject matter of any one or more of Examples 1-8optionally include wherein the outer sleeve has a radius of curvatureconfigured to mate with an outer surface of the head of the bone anchor.

In Example 10, the subject matter of any one or more of Examples 1-9optionally include wherein the cam includes a hinge channel configuredto receive the living hinge of the lever therein.

Example 11 is an anchor tower couplable to a bone anchor, the anchortower comprising: first and second extenders, each extender couplable toopposing sides of a bone anchor and each extender comprising: an outersleeve extending along a longitudinal axis from a proximal portion to adistal portion, the distal portion engageable with a head of a boneanchor; an inner sleeve extending along the longitudinal axis from aproximal portion to a distal portion, the inner sleeve nestable withinthe outer sleeve; and a cam engageable with the outer sleeve and theinner sleeve, the cam operable to secure the inner sleeve and the outersleeve to the head of the bone anchor; and a cap comprising: a bodyincluding a proximal portion and an opposite distal portion securable tothe proximal portions of the inner sleeves of the first and secondextenders; a knob coupled to the proximal portion of the body, the knobrotatable with respect to the body; and a piston located at leastpartially within the body and coupled to the knob, the pistontranslatable relative to the body in response to rotation of the knob,the piston engageable with the inner sleeves to secure the inner sleevesto the cap.

In Example 12, the subject matter of Example 11 optionally includeswherein the proximal portion of the inner sleeve of each of the firstand second extenders includes a proximal projection extending radiallyoutward therefrom.

In Example 13, the subject matter of Example 12 optionally includeswherein the distal portion of the cap includes a pair of eyes configuredto engage respective proximal projections of each inner sleeve therein.

In Example 14, the subject matter of Example 13 optionally includeswherein the body of the cap includes an internal threaded portion andwherein the piston includes an external threaded portion threadablyengageable with the internal threaded portion of the body, the knobrotatable to rotate the piston to translate the piston distally toengage each inner sleeve to force the proximal projection of each of thefirst and second extenders radially outward into the pair of eyes tosecure the cap to the extenders.

In Example 15, the subject matter of Example 14 optionally includeswherein the body further comprises a pair of pins.

In Example 16, the subject matter of Example 15 optionally includeswherein the proximal portion of each inner sleeve includes a pin boreextending radially through the proximal portion, each pin boreconfigured to receive one of the pins therein when the piston forces theinner sleeves outward.

In Example 17, the subject matter of any one or more of Examples 11-16optionally include wherein a distal portion of the piston includes apiston chamfer and wherein the proximal portion of the inner sleeveincludes a sleeve chamfer extending radially inward from a proximal lendof the proximal portion, the sleeve chamfer configured to engage thepiston chamfer when the piston is translated to engage the innersleeves.

Example 18 is an anchor tower couplable to a bone anchor, the anchortower comprising: a first extender couplable to a bone anchor, theextender comprising: a first outer sleeve extending along a longitudinalaxis, the distal portion engageable with a head of a bone anchor; afirst inner sleeve extending along the longitudinal axis, the firstinner sleeve nestable within the first outer sleeve; and a first camengageable with the first outer sleeve and the first inner sleeve, thefirst cam operable to secure the first inner sleeve and the first outersleeve to the head of the bone anchor; and a second extender couplableto a bone anchor, the extender comprising: a second outer sleeveextending along the longitudinal axis, the distal portion engageablewith the head of the bone anchor opposite the first outer sleeve; asecond inner sleeve extending along the longitudinal axis, the secondinner sleeve nestable within the second outer sleeve; and a second camengageable with the second outer sleeve and the second inner sleeve, thesecond cam operable to secure the second inner sleeve and the secondouter sleeve to the head of the bone anchor; and a cap comprising: abody including a proximal portion and an opposite distal portionsecurable to the first inner sleeve and the second inner sleeve of thefirst and second extenders, respectively; a knob coupled to the proximalportion of the body, the knob rotatable with respect to the body; and apiston located at least partially within the body and coupled to theknob, the piston translatable relative to the body in response torotation of the knob, the piston engageable with the first inner sleeveand the second inner sleeve to force the first inner sleeve and thesecond inner sleeve outward to engage the body to secure the innersleeves to the cap.

In Example 19, the subject matter of Example 18 optionally includeswherein the proximal portion of the inner sleeve of each of the firstand second extenders includes a proximal projection extending radiallyoutward therefrom.

In Example 20, the subject matter of Example 19 optionally includeswherein the distal portion of the cap includes a pair of eyes configuredto engage respective proximal projections of each inner sleeve therein.

In Example 21, the apparatuses or method of any one or any combinationof Examples 1-20 can optionally be configured such that all elements oroptions recited are available to use or select from.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments can be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1-20. (canceled)
 21. An anchor extender couplable to a bone anchor, theanchor extender comprising: an outer sleeve extending along alongitudinal axis from a proximal portion to a distal portion, thedistal portion engageable with a head of a bone anchor; an inner sleeveextending along a longitudinal axis from a proximal portion to a distalportion, the inner sleeve nestable within the outer sleeve; and a lockengageable with the outer sleeve and the inner sleeve, the lockincluding a cam rotatable to translate the inner sleeve relative to theouter sleeve between a locked position and an unlocked position and alever couplable to the cam, wherein the lever rotates the cam to securethe cam in the locked position and includes a living spring engageablewith the cam to bias the lever away from the outer sleeve.
 22. Theanchor extender of claim 21, wherein the proximal portion of the outersleeve includes an outer bore extending therethrough substantiallyorthogonally to the longitudinal axis, the outer bore configured toreceive the cam therein.
 23. The anchor extender of claim 22, whereinthe cam includes a boss extending substantially orthogonally to thelongitudinal axis, wherein the inner sleeve includes an inner borealignable with the outer bore, the inner bore configured to receive theboss therein.
 24. The anchor extender of claim 21, wherein the distalportion of the outer sleeve includes a distal hook extending radiallyinward and engageable with a notch in an outer surface of the head ofthe bone anchor.
 25. The anchor extender of claim 24, wherein the distalportion of the inner sleeve includes a distal projection extendingaxially distally and insertable into a bore in a proximal portion of ahead of the bone anchor when the inner sleeve is in the locked position.26. The anchor extender of claim 25, wherein engagement of the distalhook with the notch of the head in the unlocked position aligns thedistal projection with the bore of the proximal portion of the head. 27.The anchor extender of claim 21, wherein the inner sleeve includeschamfered radially edges extending along the longitudinal axis andwherein the outer sleeve includes a pair of opposing rails configured toreceive the chamfered radially edges therein to create a slidingengagement between the inner sleeve and the outer sleeve.
 28. The anchorextender of claim 21, wherein the outer sleeve has a radius of curvatureconfigured to mate with an outer surface of the head of the bone anchor.29. The anchor extender of claim 21, wherein the cam includes a hingechannel configured to receive the living spring of the lever therein.30. An anchor tower couplable to a bone anchor, the anchor towercomprising: first and second extenders, each extender coupleable toopposing sides of a bone anchor and each extender comprising: an outersleeve extending along a longitudinal axis from a proximal portion to adistal portion, the distal portion engageable with a head of a boneanchor; an inner sleeve extending along the longitudinal axis from aproximal portion to a distal portion, the inner sleeve nestable withinthe outer sleeve, the proximal portion including a proximal projectionextending radially outward therefrom; and a cam engageable with theouter sleeve and the inner sleeve, the cam operable to secure the innersleeve and the outer sleeve to the head of the bone anchor; and a capcomprising: a body including a pair of pins, a proximal portion, and anopposite distal portion securable to the proximal portions of the innersleeves of the first and second extenders; a knob coupled to theproximal portion of the body, the knob rotatable with respect to thebody; and a piston located at least partially within the body andcoupled to the knob, the piston translatable relative to the body inresponse to rotation of the knob, the piston engageable with the innersleeves to secure the inner sleeves to the cap; and wherein the proximalportion of each inner sleeve includes a pin bore extending radiallythrough the proximal portion, each pin bore configured to receive one ofthe pair of pins therein when the piston forces the inner sleevesoutward.
 31. The anchor tower of claim 30, wherein the distal portion ofthe body includes a pair of eyes configured to engage respectiveproximal projections of each inner sleeve therein and wherein the bodyof the cap includes an internal threaded portion and wherein the pistonincludes an external threaded portion threadably engageable with theinternal threaded portion of the body, the knob rotatable to rotate thepiston to translate the piston distally to engage each inner sleeve toforce the proximal projection of each of the first and second extendersradially outward into the pair of eyes to secure the cap to theextenders.
 32. The anchor tower of claim 31, wherein a distal portion ofthe piston includes a piston chamfer and wherein the proximal portion ofthe inner sleeve includes a sleeve chamfer extending radially inwardfrom a proximal end of the proximal portion, the sleeve chamferconfigured to engage the piston chamfer when the piston is translated toengage the inner sleeves.
 33. An anchor extender couplable to a boneanchor, the anchor extender comprising: an outer sleeve extending alonga longitudinal axis from a proximal portion to a distal portion, thedistal portion engageable with a head of a bone anchor; an inner sleeveextending along a longitudinal axis from a proximal portion to a distalportion, the inner sleeve nestable within the outer sleeve; and a lockengageable with the outer sleeve and the inner sleeve, the lockincluding a cam disposable in the outer sleeve and rotatable therein,the cam rotatable to translate the inner sleeve relative to the outersleeve between a locked position and an unlocked position, the lockcomprising: a lever couplable to the cam, operable to rotate the cam,and including a living spring engageable with the cam to bias the leveraway from the outer sleeve, the cam including a boss extendingsubstantially orthogonally to the longitudinal axis, and the camincluding a circumferential groove; and wherein the outer sleeveincludes a collar, the collar configured to receive a pin therethroughto engage the circumferential groove to guide rotation of the camrelative to the outer sleeve.
 34. The anchor extender of claim 33,wherein the distal portion of the outer sleeve includes a distal hookextending radially inward and engageable with a notch in an outersurface of the head of the bone anchor.
 35. The anchor extender of claim34, wherein the proximal portion of the outer sleeve includes an outerbore extending therethrough substantially orthogonally to thelongitudinal axis, the outer bore configured to receive the cam therein,and wherein the inner sleeve includes an inner bore alignable with theouter bore, the inner bore configured to receive the boss therein. 36.The anchor extender of claim 35, wherein the distal portion of the innersleeve includes a distal projection extending axially distally andinsertable into a bore in a proximal portion of the head of the boneanchor when the inner sleeve is in the locked position.
 37. The anchorextender of claim 36, wherein engagement of the distal hook with a notchof the head in the unlocked position aligns the distal projection withthe bore of the proximal portion of the head.
 38. The anchor extender ofclaim 33, wherein the inner sleeve includes chamfered radially edgesextending along the longitudinal axis and wherein the outer sleeveincludes a pair of opposing rails configured to receive the chamferedradially edges therein to create a sliding engagement between the innersleeve and the outer sleeve.
 39. The anchor extender of claim 33,wherein the outer sleeve has a radius of curvature configured to matewith an outer surface of the head of the bone anchor.
 40. The anchorextender of claim 33, wherein the cam includes a hinge channelconfigured to receive the living spring of the lever therein.